Composite optical disc having both a data read-only area and a data rewritable area, and a recording/reproducing system for use therewith

ABSTRACT

A composite read-only and rewritable type optical disc, and a disc drive apparatus for reading/writing data into the disc. The optical disc has a plurality of sectors forming a data read-only area and a write/read area. The disc includes a recording film formed over its entire surface by which data can be recorded on the disc. Each area has track sectors each having a sector identifier portion in which address information is recorded and a data field portion to record data. Data-field identification flags indicative of the read-only area and the write/read area are recorded in the respective identifier portions. On reading or writing this optical disc, the data field identification flag is detected to identify the kind of related area, i.e., whether it is a read-only area or a write/read area. Thus, it is possible to avoid erroneous recording of data into the read-only area. Upon executing a reading operation, waveform equalization and binary-clipping level of reproduction signals can be well controlled. The gain of the servo loop can be switched. The track searching operation can be stably performed. The reading and writing of data with respect to the data write/read area can be improved.

This is a division of application Ser. No. 353,171 filed May 17, 1989(which issued as U.S. Pat. No. 5,023,854 on Jun. 11, 1991), which inturn is a continuation of Ser. No. 007,641 filed Jan. 28, 1987(abandoned).

BACKGROUND OF THE INVENTION

The present invention relates to an optical disc on and from which datais recorded and reproduced and to a disc drive apparatus for writing andreading data into and from such an optical disc and, in particular, toan optical disc in which data can be additionally written on a read onlytype optical disc and to a drive apparatus for writing and reading datainto and from such an optical disc. As an external memory which canstore a large amount of data, attention is paid to an optical disc driveapparatus using a read-only type optical disc (hereinafter, referred toas an R/O disc) in which data is recorded on a disc-shaped plasticmaterial in the form of concave and convex pits or phase structure ofthe submicron order and the data is reproduced by irradiating a laserbeam having a diameter of about 1 μm.

The R/O disc is formed in the following manner. The data modulatedconcave and convex pits of the submicron order are formed on a plasticresin made of polycarbonate or the like having a thickness of 1.2 mm. Areflecting layer made of aluminum or the like is evaporation depositedon the surface of the plastic resin and thereafter, a protecting layeris coated on the reflecting layer. Although the R/O disc has a diameterof 12 cm and a memory capacity of hundreds of megabytes, additional datacannot be recorded.

Various uses and applications of such an R/O disc are considered due tovarious advantages such that its memory capacity is large, random accesscan be performed, a number of duplicate discs can be easily produced,and the cost is low. For example, the R/O disc can be used as a disc inwhich the dictionary or font patterns for use in data base or wordprocessors are stored, or as a disc in which programs or operatingmanually of computers are stored.

However, the foregoing R/O disc is of the read-only type and ismanufactured in a particular factory. Therefore, it is impossible forthe user to use the disc by adding his preferred extra data to thedictionary or font patterns of the data base or word processor whichwere supplied in the R/O disc. In addition, patch cannot be added inorder to correct bug in the program. Therefore, the R/O disc has aproblem such that its application field in computers is limited.

SUMMARY OF THE INVENTION

In consideration of the foregoing problems, it is an object of thepresent invention to provide an optical disc in which the user canrecord additional data to the R/O disc and from which the user can wellreproduce the data in the read-only area and those in the data recordingarea and further to provide a drive apparatus for writing and readingdata into and from such an optical disc.

According to the present invention, an optical disc is formed in thefollowing manner. Namely, a recording material is formed in all of thetracks. A plurality of sectors are formed in the tracks. A sector has asector identifier for identifying the sector in which addressinformation is recorded and a data field portion to record data. A datafield identification flag indicative of a read-only area or a datarecording/reproducing area is recorded in the respective sectoridentifier. In this optical disc, the data field identification flag isdetected. The kind of the area of a current sector is discriminated onthe basis of the detected data field identification flag. Thus,erroneous recording of data into the read-only area can be prevented.The waveform equalization and binary-clipping level of the reproduceddata signal can be controlled upon reproduction of the data. The gain ofthe servo loop can be switched. The track searching operation can bestably performed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) are a plan view and a cross-sectional view of anembodiment of an optical disc according to the present invention,respectively;

FIG. 2 shows signal formats for the embodiment;

FIG. 3(a-t) shows enlarged cross sectional views of tracks of theoptical disc and corresponding reproduced signal waveforms in theembodiment;

FIG. 4 is an external view of an embodiment of a cartridge of theoptical disc of the invention;

FIG. 5 is a block diagram of an embodiment of a write protecting(enabling or disabling) circuit of an optical disc drive apparatus ofthe invention;

FIG. 6 is a block diagram of another embodiment of a write protecting(enabling or disabling) circuit of an optical disc drive apparatus ofthe invention;

FIG. 7(a, b) exemplarily shows track allocation diagrams of the opticaldisc of the invention;

FIG. 8 is a block diagram of an embodiment of a data reading circuit forperforming the data reproduction on the optical disc in the optical discdrive apparatus of the invention;

FIG. 9 is a block diagram of an optical detecting system and a servosystem in the embodiment;

FIG. 10 is a block diagram of an embodiment of a servo circuit of theoptical disc drive apparatus of the invention;

FIG. 11 is a block diagram of the optical detecting system, servosystem, and search system in the embodiment; and

FIGS. 12(a) and 12(b) are a plan view and a a cross-sectional view ofanother embodiment of an optical disc of the present invention,respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an external view of an embodiment of an optical disc of thepresent invention. FIG. 1(a) is a plan view of the optical disc and FIG.1(b) is a cross sectional view taken along the line A--A' in FIG. 1(a).In FIG. 1, reference numeral 1 denotes an optical disc; 2 is a centerhole adapted to attach the optical disc to a disc motor; 3 indicatesdata recording area of a plurality of tracks consisting of sectorshaving data field portions DF in which no data is recorded; 4 dataread-only area of a plurality of tracks consisting of sectors havingdata field portions DF in which data has previously been recorded; 5 adisc substrate made of polycarbonate resin or the like; 6 tracks whichare formed as grooves in the disc substrate; 6a data recording area; 6bdata read-only area; 7 a recording material in which signals can beoptically or thermally recorded by a laser beam; and 8 a protectinglayer to protect the recording material 7. S₀, S₁, S₂, . . . , S_(n)denote sectors; ID represents sector identifier portions in which theaddress information of the sectors S₀ to S_(n) is recorded; and DFindicates the data field portions to record data.

The optical disc 1 is formed in the following manner. The groove-shapedtracks 6 are formed in the disc substrate 5. Each track is divided intoa plurality of sectors comprising the sector identifier portions ID anddata field portions DF. The recording material 7 is uniformlyevaporation-deposited on the disc substrate 5 having the tracks 6 so asto cover the whole surface of the disc.

By irradiating a recording laser beam of a large power onto therecording material 7 in the data recording area 3, the beam signal canbe recorded in the data recording area as changes in reflectance or aformation of holes. If the recording material 7 is a magneto-opticmaterial, by reversals of the magnetic domain, the recorded signal canbe read out on the basis of the rotation of the polarizing wave front ofthe reflected light by the Faraday effect. In the data read-only area 4,the recording material 7 functions as a reflecting film to reflect areading laser beam of weak power.

As described above, according to this embodiment, by forming the samerecording material 7 in the data read-only area 4 and in the datarecording area 3, read-only type optical discs having recordable sectorscan be easily manufactured.

FIG. 2 is an explanatory diagram of data field identification flags F(F₁, F₂) in the sector identifier portions ID of the optical disc in theforegoing embodiment.

In the diagram, FIG. 2(a) shows a sector format of the data read-onlyarea 4 in which data is recorded as concave and convex forms in the datafield portion DF. FIG. 2(b) is a sector format of the data recordingarea 3 in which the data field portion DF is the groove-shaped tracksegment of a uniform depth. FIG. 2(c) shows a practical example of anaddress ADR, a data field identification flag F₁, and error detectioncode CRC in the data read-only area 4. FIG. 2(d) shows a practicalexample of an address ADR, a data field identification flag F₂, anderror detection code CRC in the data recording area 3.

In the sector identifier portion ID, PR denotes a preamble to reproducea clock; AM is an address mark to indicate the start of the addressinformation; ADR is the address; F₂ the data field identification flagindicative of the data recording area 3; F₁ the data fieldidentification flag indicative of the data read-only area 4; CRC theerror detection code such as cyclic-redundancy code or the like; and POa postamble. G₁ and G₂ denotes gaps in which no information is recordedin order to absorb the fluctuation in the rotation of the optical disc.

In the data field portion DF, SYNC denotes a clock sync signal toreproduce a clock; DM is a data mark indicative of the start of thedata; DATA indicates data; ECC represents error detection/correctioncode; and RESYNC represents a RE-SYNC pattern to make wordsynchronization for data demodulation.

The address ADR comprises; two bytes of the track address information; atrack address (high byte) TA (H); a track address (low byte) TA (L); andsector address information SA. The operation with the examples of FIG. 2will now be described hereinbelow.

When the optical disc drive apparatus reads out an arbitrary sectoridentifier portion ID, the data field identification flag F are detectedas, for example, F₁ =1 or F₂ =0 as shown in FIGS. 2(c) or 2(d). Theoptical disc drive apparatus immediately knows whether this sectorbelongs to that with the data read-only area 4 or that with the datarecording area 3 and performs controls such as prevention of erroneouswriting of data, waveform equalization of the reproduction signal,optimization of the servo loop gain, and stabilization of the search ofa desired track, which will be explained hereinafter.

FIG. 3 is an enlarged cross sectional view of the tracks of the opticaldisc in the foregoing embodiment. FIG. 3(a) illustrates a partialenlarged diagram of the sector identifier portion ID, gap G₁, and datafield portion DF in the data read-only area 4. FIG. 3(b) shows a partialenlarged diagram of the sector identifier portion ID, gap G₁, and datafield portion DF in the data recording area. FIG. 3(c) is a waveformdiagram of the reproduction signal in the data recording area of FIG.3(b).

In FIG. 3, the tracks in the data read-only area 4 and data recordingarea 3 are formed with the same recording material 7. The addressinformation of the sector is formed in each sector identifier portion IDby concave and convex pits P. In addition, the data is formed in thedata field portion DF in the data read-only area 4 by concave and convexpits P similarly to the sector identifier portion ID. The data fieldportions DF in the data recording area 3 are grooves of a uniform depth,wherein data recorded by the user is recorded in the recording material7 as dots D such as of reflectance changes, reversals of the magneticdomain, holes, or the like.

As shown in FIG. 3(c), the reproduction amplitude A₁ of the pit portionP differs from the reproduction amplitude A₂ of the dot portion D. Whenthe phase change recording material is evaporation-deposited such thatthe depth of a groove is equal to 1/8 of the wavelength, in general, thefollowing relationship of the reflectances is satisfied: namely, thereflectance of the dot portion>the reflectance of the land portion>thereflectance of the pit portion. On the other hand, since the opticalcharacteristics of the pit portion and land portion differ, thefrequency characteristics of the reproduction signals may also differ.Therefore, the waveform equalization amounts and the binary-clippinglevels need to be controlled in accordance with the data recording area3 and data read-only area 4.

Since the same recording material 7 is formed in the areas 3 and 4,there is no need to separately form the reflecting layer such asaluminum or the like in the area 4 and to form the recording material 7in the area 3 as in conventional optical discs. Therefore, it isunnecessary to specially form buffer portions in which no data isrecorded at boundary regions between the areas 3 and 4.

FIG. 4 is an external view of an embodiment of a cartridge of theoptical disc of the invention. In FIG. 4, reference numeral 10 denotes acartridge; 11 is a shutter of a window for recording and reproducting inorder to irradiate a laser beam onto the optical disc 1; 12 is a discidentifier to identify the kind of disc such as R/O (read only) type,W/O (write once) type, W/E (erasable) type, or the like; and 13 a writeprotecting notch to set the permission/inhibition of the writing of thedata into the data recording area 3 of the optical disc 1.

FIG. 5 shows a block diagram of an embodiment of a write protectingcircuit to permit/inhibit the writing of the data into the optical discin the optical disc drive apparatus of the invention.

Reference numeral 14 denotes a disc identifier detecting section todetect the disc identifier 12 of the cartridge; 15 is a write protectingnotch detecting section to detect the setting of the write protectingnotch 13 and to output a write protection detection signal 101; 16 anaddress reading section to read the address information from the sectoridentifier ID of a current sector and to output a data fieldidentification flag signal 102; 17 a decoder section for decoding theoutput of the disc identifier detecting section 14 and for generating anR/O disc detection signal 100; 18 and 19 two-input NAND gates; 21 aninverter; 20 and 22 AND gates; 23 a laser driving section; and 24 asemiconductor laser.

The operation of the optical disc drive apparatus shown in FIG. 5 andusing the optical disc 1 and cartridge 10 shown in FIGS. 1 and 4 willnow be described hereinbelow.

When the cartridge 10 of the R/O disc 1 is set into the optical discdrive apparatus, the disc identifier detecting section 14 reads the discidentifier 12 of the cartridge 10 and interprets by the decoding section17 and outputs the R/O disc detection signal 100. The notch detectingsection 15, on the other hand, reads the setting of the write protectingnotch 13 of the cartridge 10 and outputs the write protection detectionsignal 101. Further, the address reading section 16 reads the sectoridentifier portion ID of the optical disc 1 by the laser beam andoutputs the data field identification flag F of the sector identifierportion ID as the data field identification flag signal 102. When thesignal 102 is valid and indicates the data read-only area 4, the outputof the NAND gate 18 becomes a low level by the signals 100 and 102,thereby setting a write protection signal 103 as the output of the ANDgate 20 to be valid (low level). Since the signal 103 is at a low level,a write data signal 104 as an input to the laser driving circuit 23 ismade invalid by the AND gate 22, so that the semiconductor laser 24 doesnot produce the recording power output.

When the flag signal 102 is invalid and indicates the data recordingarea 3, the output of the NAND gate 19 is set to a low level by thewrite protection detection signal 101 and by the signal of which theflag signal 102 was inverted by the inverter 21 if the signal 101indicates the inhibition of the writing, thereby setting the writeprotection signal 103 as the output of the AND gate 20 to be valid (lowlevel). Thus, it is prevented that the semiconductor laser 24 producesthe recording power output as in the case of the foregoing dataread-only area 4.

If the detection signal 101 indicates the permission of the writing, theoutput of the NAND gate 19 becomes high, thereby making the signal 103as the output of the AND gate 20 invalid (high level). Thus, the writedata signal 104 is transmitted through the AND gate 22 and drives thelaser driving section 23. The power of the semiconductor laser 24 ismodulated by the recording power output, thereby recording the writedata signal 104 into the current relevant sector.

As described above, according to the above embodiment, by providing thedata field identification flag F in the sector identifier portion ID ofthe optical disc and by providing the disc identifier and writeprotecting notch for the cartridge, the erroneous writing of data intothe data read-only area can be inhibited and at the same time, thepermission/inhibition of the writing of data into the data recordingarea can be selectively and freely set.

FIG. 6 shows a block diagram of another embodiment of a write protectingcircuit for permitting/inhibiting the writing of data into the opticaldisc drive apparatus in an information recording and reproducingapparatus of the present invention.

Reference numeral 25 denotes a write protecting notch detecting sectionfor detecting the setting of the write protecting notch 13 and foroutputting a write protection detection signal 105; 26 is an addressreading section for reading address information 107 and a data fieldidentification flag signal 110 which are included in the sectoridentifier portion ID of the sector from a reproduction signal 106; 27an address comparing section for comparing the address information 107with target address information 108; 28 a flag comparing section forcomparing the flag signal 110 with an input flag 111 generated from CPUmentioned later; 29 a data modulating section for modulating input data115; 30 a laser driving circuit section; 31 a semiconductor laser; 32 aninverter; and 33 and 34 AND gates.

The operation of the information recording apparatus shown in FIG. 6will now be described hereinbelow by use of the optical disc 1 andcartridge 10 shown in FIGS. 1 and 4.

When the cartridge 10 of the R/O disc 1 is set into the informationrecording apparatus, the write protecting notch detecting section 25reads the setting of the write protecting notch 13 of the cartridge 10and outputs the write protection detection signal 105. Further, addressreading section 26 reads the sector identifier portion ID of the opticaldisc 1 by a laser beam and outputs the address information 107 of thesector identifier portion ID to the address comparing section 27 and thedata field identification flag signal 110 to the flag comparing section28.

The section 27 compares the address information 107 with the targetaddress information 108 and transmits an address coincidence output 109to the AND gate 33.

The flag comparing section 28 compares the input flag 111 with the flagsignal 110 and outputs a flag coincidence output 112 to the AND gate 34.

First, the operation to inhibit the writing of data into the dataread-only area 4 will be explained hereinbelow.

Since the writing of data is permitted to only the data recording area3, the input flag 111 is set by the CPU to correspond to the data fieldidentification flag indicative of the data recording area 3.

Namely, in the case of the data read-only area 4, the flag signal 110differs from the input flag 111, so that the flag coincidence output 112of the flag comparing section 28 becomes invalid (low level). Therefore,even if the target address information 108 and a write command 113 areapplied in which the sector in the area 4 is used as the target sectorand the address comparing section 27 outputs the address coincidenceoutput 109 and the data modulating section 29 is made operative, a writedata signal 116 from the section 29 is blocked by the AND gate 34, andthe input to the laser driving section 30 is made invalid, therebypreventing that the semiconductor laser 31 produces the recording poweroutput. Thus, it is prevented that the data is erroneously written intothe data field portion DF of the sector in the data read-only area 4.

The operation to write data into the data recording area 3 will now bedescribed hereinbelow.

The input flag 111 is set by the CPU to correspond to the data fieldidentification flag indicative of the data recording area 3 and the flagcoincidence signal 112 becomes valid (high level).

If the write protection detection signal 105 indicates the inhibition ofthe writing (high level), a signal 117 of which the detection signal 105was inverted by the inverter 32 sets the output of the AND gate 34 to alow level, thereby preventing that the semiconductor laser 31 producesthe recording power output similarly as in the case of the foregoingdata read-only area 4. If the detection signal 105 indicates permissionto write (low level), the output of the inverter 32 becomes a highlevel. Therefore, the predetermined target address information 108 andwrite command 113 are applied. When the address comparing section 27detects a desired sector and makes the address coincidence output 109valid (high level), the AND gate 33 makes a signal 114 valid (highlevel) and the data modulating section 29 is made operative, so that theinput data 115 is modulated by the section 29 and is transmitted as thewrite data signal 116 through the AND gate 34 and drives the laserdriving section 30. Thus, the power of the semiconductor laser 31 ismodulated by the recording power output, thereby recording the writedata signal 116 into the related sector.

As described above, according to the above embodiment, by comparing thedata field identification flags F provided in the sector identifierportion ID of the optical disc together with comparing the addressinformation and by forming the write protecting notch, the erroneouswriting of the data into the data read-only area can be inhibited andthe permission/inhibition of the writing of data into the data recordingarea can be freely and selectively set.

FIG. 7 is a track allocation diagram of the optical disc of theinvention. FIG. 7(a) shows an embodiment of a track allocation which aredivided into data read-only areas 35a and 35b and a data recording area36a on the basis of sectors. This allocation is constituted by: the dataread-only area 35a constituted from sector S₀ in track 0 up to sector S₁in track 2; the data recording area 36a from sector S₂ in track 2 up tosector S₀ ; in track (i+l) and the data read-only area 35b from sectorS_(i) in track (i+l) up to sector S_(n) in track n. A dummy sector DS₁corresponding to sector S₂ in track 2 is provided in the boundarybetween the areas 35a and 36a and belongs to the data recording area36a. A dummy sector DS₂ corresponding to sector S₁ in track (i+l) isprovided in the boundary between the areas 36a and 35b and belongs tothe data read-only area 35b.

FIG. 7(b) shows an embodiment of a track allocation which are dividedinto data read-only areas 35c and 35d and a data recording area 36b onthe basis of tracks. This allocation is constituted by: the dataread-only area 35c from sector S_(o) track 0 up to sector S_(n) in track(i-l); the data recording area 36b from sector S_(o) in track i up tosector S_(n) in track (l-l); and the data read-only area 35d from sectorS_(n) in track l up to sector S_(n) in track n. Two dummy sectorsDS_(36a) and DS_(36b) corresponding to sectors S₀ and S₁ track i areprovided in the boundary between the areas 35c and 36b and belong to thedata recording area 36b. Two dummy sectors DS_(35a) and DS_(35b)corresponding to sectors S_(p) and S₁ track l are provided in theboundary between the areas 36b and 35d and belong to the data read-onlyarea 35d.

Each of the dummy sectors DS₁, DS_(36a), and DS_(36b) which belong tothe data recording areas 36a and 36b comprises: the sector identifierportion ID having the data field identification flag F indicative of thedata recording area; and the data field portion DF in which no data isrecorded. Each of the dummy sectors DS₂, DS_(35a), and DS_(35b) whichbelong to the data read-only areas 35b and 35d comprises: the sectoridentifier portion ID having the data field identification flag Findicative of the data read-only area; and the data field portion DFwhere no data is preliminarily recorded.

Referring to FIG. 7, as will be explained hereinafter, even when anerror occurs in the sector identifier portion ID of the sector in whichthe data is recorded and this sector cannot be found out, thereproduction signal can be read out of each area under the optimumreading condition by use of the data field identification flags in thesector identifier portions ID of the head dummy sectors of the dataread-only areas 35b and 35d or of the data recording areas 36a and 36b.

FIG. 8 shows a block diagram of a data reading circuit for performingthe data reproduction from the optical disc in the optical disc driveapparatus of the invention. In FIG. 8, reference numberal 37 denotes adata equalization and binary signal generating section for performingwaveform equalization to correct the deterioration of the frequencycharacteristic of the reproduction signal 106 and converting the analogsignal into a binary signal; 38 is a data demodulating section fordigitally demodulating the output of the section 37; 39 a level controlsection for generating a level control signal 118 to control thewaveform equalization amount and binary-clipping level of the section 37in response to the data field identification flag signal 110; 26 theaddress reading section for reading the address information and datafield identification flag from the sector identifier portion ID; 27 theaddress comparing section for detecting the coincidence between thetarget address signal 108 and read address signal 107 and for outputtingthe address coincidence signal 109; 40 a control CPU for producing thetarget address signal 108 to control the data demodulation for thetarget sector, for detecting the address coincidence signal 109 and foroutputting a data demodulation enable signal 119 to make the datademodulating section 38 operative; and 120 a read data signal.

The operation of the optical disc drive apparatus shown in FIG. 8 willnow be described hereinbelow.

When the optical disc 1 is set into the optical disc drive apparatus,the address reading section 26 reproduces the sector identifier portionID of the optical disc by a laser beam and reads out the addressinformation and data field identification flag of the sector identifierportion ID and outputs the address signal 107 and data fieldidentification flag signal 110.

The waveform equalization amount and binary-clipping level of theaddress reading section 26 are set to the level for the data read-onlyarea 4. By changing the level control signal 118 of the level controlsection 39, the data field identification flag signal 110 is referred toset the waveform equalization amount and binary-clipping level in thesection 37 so that the bit error rate of the read data signal 120becomes a minimum value when the reproduction signal 106 is demodulatedby the data demodulating section 38. For example, in the case of thebinary-clipping level, if the flag signal 110 indicates the dataread-only area 4, the level control signal 118 sets the binary-clippinglevel of 1/2 of the amplitude A₁ of the reproduction signal of thesector identifier portion ID in FIG. 3(c) into the data equalization andbinary signal generating section 37. On the other hand, if the flagsignal 110 indicates the data recording area, the level control signal118 sets the binary clipping level of 1/2 of the amplitude A₂ of thereproduction signal of the data field portion DF in FIG. 3(c) into thesection 37.

The control CPU 40 outputs the target address signal 108 to the addresscomparing section 27. When the read address signal 107 coincides withthe target address signal 108, the section 27 outputs the addresscoincidence signal 109. When the control CPU 40 detects the addresscoincidence signal 109, it outputs the data demodulation enable signal119 to the data demodulating section 38, thereby starting the datademodulating operation. The section 38 digitally demodulates the binarysignal supplied from the section 37 and outputs the read data signal120.

If the address coincidence signal 109 is not detected, the control CPU40 outputs the target address signal 108 having the address value of(the target address value-1) to the section 27. When the read addresssignal 107 coincides with the new target address signal 108, the section27 outputs the address coincidence signal 109. The data fieldidentification flag signal 110 which was read out of the sectorcorresponding to the target address signal 108 having the address valueof (the target address value-1) supplies the level control signal 118such as to allow section 37 to perform the optimum reading operation.Next, the control CPU 40 detects the address coincidence signal 109 andwaits for only the period of time corresponding to one sector and thenoutputs the data demodulation enable signal 119 to the data demodulatingsection 38, thereby starting the data demodulating operation of thetarget sector. The foregoing operations correspond to the cases of thedummy sectors DS₁ and DS₂ in FIG. 7(a).

Further, if an error still occurs with a sector identifier portion IDeven with the above operation with the address value of (the targetaddress value-1), the address value of (the target address value-2) maybe given to the target address signal 108 by use of the allocation withtwo dummy sectors DS_(36a) and DS_(36b) or DS_(35a) and DS_(35b) shownin FIG. 7(b). With the allocation, the control CPU 40 waits for only theperiod of time corresponding to two sectors after the addresscoincidence signal 109 was detected. Then, the CPU 40 outputs the datademodulation enable signal 119 to the section 38, thereby reading outthe target sector. By producing the target address signals 108indicative of the address value of (the target address value-1) and theaddress value of (the target address value-2), data can be recovered andreproduced even from data read-only area or recording area with twocontinuous defective sector identifiers. Therefore, the optimumbinary-clipping level and waveform equalization amount can be set withthe high reliability and the data reading reliability can be increased.

As described above, according to the above embodiment, in order todetect the data field identification flags of the sector identifierportions of the optical disc the dummy sectors are provided for the headsectors of the data read-only area and the data recording area, and thedata recovery operations can be executed with those dummy sectorsagainst possible errors caused in sector identifier portions. Therefore,the data field identification flags of all the sectors in the currentrelated area can be detected with high reliability. The data readingconditions can be controlled so as to correct the differences of thereproduction signal amplitudes and of the frequency characteristics ofthe data field portions. In this manner, the data can be read out of theR/O disc having the data recordable area with high reliability.

FIG. 9 shows a block diagram of the optical detecting system and theservo system in the optical disc drive apparatus. Reference numeral 1denotes the optical disc for recording and reproducing information; 41is a semiconductor laser of a wavelength λ; 42 and 43 condenser lenses;44 a polarizing beam splitter; 45 a 1/4 wavelength plate; 46 a focusinglens; 47 a focusing lens actuator; 48 a mirror to separate the reflectedlight; 49 a focusing photodetector; 50 a tracking photodetector; 51 and52 differential amplifiers; 53 a focus servo circuit section; and 54 atracking servo circuit section.

The light emitted from the semiconductor laser 41 progresses asindicated by broken lines and passes through the focusing lens 46 and isfocused onto the track of the disc, thereby performing the recording andreproducing operations. The reflected light then passes through the beamsplitter 44 and condenser lens 43 as shown by solid lines and isseparated by the mirror 48. The separated light enters the focusingphotodetector 49 and tracking photodetector 50, respectively. Thus, afocus error signal 121 and a tracking error signal 122 are outputtedthrough the difference amplifiers 51 and 52, respectively. Drive signals123 and 124 of the focusing lens actuator are outputted by the focusservo circuit 53 and tracking servo circuit 54 and the focusing lens 46is driven to the optimum position such that the error signals 121 and122 become zero. In this manner, the well-known focus control andtracking control are performed.

FIG. 10 is a detailed diagram of the focus servo circuit section 53. Inthis diagram, the focus error signal 121 derived from the focus servophotodetector 49 passes through a gain switching section 55 and a phasecompensating section 56 and is supplied to a driving circuit section 57.The drive signal 123 is outputted to drive the focusing lens 46 so thatthe focus error signal 121 becomes zero. The flag signal 110 is sent tothe gain switching section 55 in the focus servo circuit section 53,thereby switching the gain such that the loop gain of the focus servobecomes constant.

In this manner, in the data recording area 3, it is possible toeliminate the instability of the servo characteristic due to the largeamplitude of the focus error signal and the large loop gain of the focusservo because of the large reflectance. In the data read-only area 4,the loop gain of the focus servo decreases since the reflectance issmall, and the deterioration of the servo tracking performance can becompensated, and the loop gain can be always made constant.

With respect to the tracking servo, the stable tracking servo can bealso performed by constituting the circuit similarly to the foregoingfocus servo.

As described above, according to the embodiment, by switching the gainsuch that the loop gains of the focus and the tracking servo becomeconstant in each of the data read-only area and the data recording area,the optimum recording and reproducing operations of the R/O disc havingthe data recordable area can be executed.

FIG. 11 shows a block diagram of the optical detecting system, servosystem, and search system in the optical disc drive apparatus of theinvention. In FIG. 11, the parts and components indicated at referencenumerals 41 to 54 are the same as those shown in FIG. 9. Referencenumeral 58 denotes a differential amplifier; 59 is a traversed tracknumber counting circuit section; 60 a comparator section for comparingthe target track with the output of the counting circuit section 59 inorder to detect their coincidence; 61 a target track address registerfor storing the target track address value; 62 a linear motor drivingcircuit section; and 63 a linear motor to move an optical headsurrounded by a broken line.

A focus sum signal 125 of the differential amplifier 58 is input to thecounting circuit section 59 together with the tracking error signal 122.As disclosed in U.S. Pat. No. 4,484,319, "Apparatus for locating a trackon disc-like optical information carriers" herein incorporated byreference, the true number of tracks which are traversed by the laserbeam is counted and this true track number is obtained by correcting apossible eccentricity of the optical disc 1 from the polarity of thetracking error signal 122 using the phase of the focus sum signal 125 asa reference signal.

The rough search by the linear motor 63 is executed in a manner suchthat the value of the target track address register section 61 iscompared with the output of the counting circuit section 59 by thecomparing section 60 and when they coincide, the driving of the linearmotor driving circuit section 62 is stopped.

After completion of the rough search, the tracking servo circuit 54 ismade operative, thereby tracing a predetermined track.

When the address of the track which is being tracked is read out and ifit differs from the target track, the track is again searched. Thedifference between the searched track and the target track is called thesearch error and this error is caused by the possible erroneous countingof the number of traversed tracks. If the search error is smaller than apredetermined value, the focusing lens actuator 47 is driven by thetracking servo circuit 54 to skip the tracks, thereby performing a finesearch to move to the target track while checking the track address bythe signal 107. If the search error is large, the linear motor is againdriven and the rough search is reexecuted.

FIG. 12 is an external view of an embodiment of the optical disc of theinvention. In the diagram, reference numerals 64a and 64b denote guardareas where no data is recorded. In FIG. 12, since no data is recordedin the guard areas 64a and 64b, these areas are not used for the searchstart address nor for the search target address. Therefore, if the guardareas 64a and 64b provided in the data read-only area 4 and datarecording area 3 are larger than the numbers of erroneously searchedtracks, when the searching operation is shifted from the data read-onlyarea 4 (or data recording area 3) to the data recording area 3 (or dataread-only area 4), the target area portion, in this just-mentioned case,the track in the area 3 (or area 4) can be accessed to after completionof the rough search by the linear motor 63 even in the worst case.Therefore, the fine search can be executed in the same portion of thedata recording area 3 (or data read-only area 4), so that the problem ofinstability in the tracking servo can be solved.

On the other hand, if none of the guard areas 64a and 64b is provided oreven if they are provided, when they are smaller than the track numberdue to the search error, it is impossible to accurately determinewhether a track detected after completion of the rough search by thelinear motor 63 belongs to the data recording area 3 or to the dataread-only area 4. When the searching operation is shifted from the area4 (or area 3) to the area 3 (or area 4), if there occurs a case where aportion near the boundary between the areas 3 and 4 is accessed to bythe first trial of the search and the boundary is skipped over by trackjump of the subsequent fine search, the tracking becomes unstable by alarge change in reflected light amount and this may cause the resultsuch that the tracks are irregularly skipped and many trials are neededto skip a predetermined number of tracks or that the target track cannotbe accessed. Therefore, in the search of tracks in the areas 3 and 4, byproviding the guard areas over the search errors in the boundary betweenthe areas 3 and 4, the area to which a target track belongs can becertainly accessed by the first trial of the search, so that any desiredtrack can be stably searched.

As described above, according to the above embodiment, by respectivelyproviding the guard areas having no data in the boundary between thedata read-only area and the data recording area of the optical disc, anydesired track of the R/O disc having the data recordable area can bestably searched.

As described above, according to the invention, it is possible toprovide an optical disc in which the user can freely record data intothe R/O disc, and the data read-only area and the data recording areacan be stably searched and the data can be accurately read out and toprovide a drive apparatus of such an optical disc. The practical effectsof the invention are great.

What is claimed is:
 1. An optical system comprising:(a) an optical discplayer; and (b) an optical disc; said optical disc including a pluralityof tracks comprising a plurality of sectors, each sector including asector identifier portion having sector address information recordedtherein and a data field portion for data recording/reproducing, whereindata is reproduced and/or recorded by irradiating a laser beam onto alight-sensitive recording material formed on the tracks; said opticaldisc player including a data recording and reproducing optical head, alinear motor and a track search means for shifting said optical headalong said disc by said linear motor to perform a track coarse searchoperation and a track fine search operation by causing a laser beamemitted by a laser source of the optical head to jump tracks, saidplayer having a characteristic maximum possible number of erroneouslysearched tracks during said coarse search operation; said plurality ofsectors of said optical disc comprising: a data read-only areacomprising a plurality of first sectors having a said data field portionin which data has been recorded in concave and convex phase structure;and a data recording/reproducing area comprising a plurality of secondsectors having a said data field portion in which data can be recorded,each of said first and second sectors having address information and adata field identification flag recorded in concave and convex phasestructure in the sector identifier portion thereof, said flag being setin one of a first state and a second state, said first state indicatingthat a sector in which a said flag is recorded has a data read-only areaand said second state indicating that a sector in which a said flag isrecorded has a data recording/reproducing area; and said optical diskfurther comprising first and second guard areas interposed between saiddata read-only area and said data recording/reproducing area, said firstguard area comprising a first number of said tracks having a concave andconvex phase structure substantially identical to that of said dataread-only area and said second guard area comprising a second number ofsaid tracks in which data can be recorded as in said datarecording/reproducing area, and both said first number and said secondnumber being greater than said characteristic maximum possible number oferroneously searched tracks of said disk player.